p-Cycles offer a promising new approach to optical network survivability, summed up by the notion of “ring like speed with mesh-like efficiency”. Being based on closed cyclic paths of protection capacity, p-cycles offer ring-like speed and pre-configured simplicity but are essentially as efficient as span-restorable mesh networks thereby offering three to six times greater demand-carrying capability than rings for a given transmission capacity. Unlike rings, p-cycles protect straddling failures as well as on-cycle failures and allow working paths to take shortest routes. This combination of properties, suggest the prospect of an optical network that is survivable to any single span failure with as little as ˜35% redundancy, depending on graph topology and demand pattern. In contrast, optical rings and fiber-level cycle double covers are at best 100% redundant (and often much higher) in terms of spare and unused working capacity. p-Cycles also provide the much-touted “50 ms” speed, because only two nodes do any switching, and the failure-dependent local switchover actions are BLSR-like and known in advance.
p-Cycles are like rings but with support for the protection of straddling span failures as well as the usual ring-protection of spans of the ring itself (on-cycle failures). A straddling span has its end-nodes on the p-cycle, but is not itself part of the p-cycle, like a chord on a circle. With p-cycles, working paths also take any desired route over the graph and are not constrained to follow ring routings. When an on-cycle span fails, the surviving arc of the cycle is used just as in a BLSR ring. However, the same p-cycle is also accessible to support restoration of a straddling span failure, in which case two restoration paths are available from each unit of p-cycle protection capacity. In the limit of a full set of straddling span relationships, an N-hop p-cycle can protect up to N(N−2) units of working capacity, making it up to N−2 times more efficient than a corresponding ring. However, the design of a min-cost set of p-cycles to protect a given set of working flows is an NP-hard problem. The basic formulation generates large problem files that can be difficult to solve to optimality, primarily because of the size of the set of candidate cycles to consider. This is especially true when the jointly optimized problem or the consistent wavelength assignment problem is attempted. Some investigators are pursuing pure heuristics for the problem, and a fully distributed p-cycle forming process is known. This invention seeks to provide an improved method for designing a telecommunications network that optimizes routing of working demands and spare capacity, that is, that provides a solution to what is known as the joint optimization problem.